Electromechanical vibratory system and apparatus



Oct. 23, 1934. FlCHANDLER 1,977,939

ELECTROMECHANICAL VI BRATORY SYSTEM AND APPARATUS I Filed Oct. 5. 1931 Patented Oct. 23, 1934 um'rso STATES ELECTROMECHANICAL VIBRATORY SYSTEM AND APPARATUS Carl Fichandler, New York, N. Y. Application October 5, 1931, Serial No. 567,122 Claims. (01. 250-446) j;

The present invention relates to the production ofv mechanical and electrical vibrations or oscillations and to the resultant of interacting mechanical and electrical vibrations or oscillations. 5 It is well known that oscillations of mechanical vibrators can be produced and maintained by electrical excitation. Perhaps the best known example is the interrupter used in bells, buzzers and the like. For the production of constant freduen'cy vibration the interrupter is not well suited, because the variable mechanical load imposed upon the vibrator by the movement of .the contact arm results in vibrations of varying frequency and excessive harmonic content.

is to provide a method and means for producing mechanical and electrical vibrations or oscillations of constant frequency and of undistorted wave form. According to this invention an oscillating electrical and mechanical vibration is produced under the control of a mechanical and/or electrical resonator such as a reed, tuning fork, piezo-electric crystal, and the like.

A refinement of the interrupter method involves the excitation of a tuning fork by current variations produced by the pressure of the fork on a microphone. The disadvantagesdue to the variable mechanical load, as in the interrupter method, and the initial and replacement costs of the microphone are highly objectionable.

Another object of the present invention is to obviate the disadvantages of the tuning fork and microphone type of oscillating vibrator.

The highest quality type of tuning fork oscillator which is known to the art involves the use of thermionic tubes. In this type of oscillator, the action involves electric induction to the grid circuit of an amplifier tube, the plate circuit of which feeds back energy to the vibrator. In this arrangement, the vibrator serves as a tuned coupling link in an oscillatory audion circuit. While the quality of the tuning fork and tube oscillator i'shigh, this oscillator is comparatively complicated and bulky and involves the initial and replacement costs of the tubes.

A further object of this invention is to provide an oscillating'vibrator, the quality of which is at least as high as that of the tuning fork and tube oscillator but which does notinvolve thermionic tubes or the like Whereby tO provide a high-quality oscillatingvibrator of simple construction and at low cost.

A further object is to provide a sharply tuned amplifier for harmonlmmechanical or, electrical vibrations without the use of thermionic tubes orthelike. L

A further object is to provide a simple and stable source of musical tones for sound signals, electro-musical instruments, and the like;

One object of the present invention, therefore,-

A still further object of the invention is generally to improve oscillating vibrators.

The invention canbest be understood by reference to the following description considered in connection with the accompanying drawing, in whichFigure l is a more or less diagrammatic view of one embodiment of the invention, and Figure 2is a similar view of. another mbodiment.

As shown in Figure 1, there is provided an electromagnetic core 1 having poles 1a and 1b spaced to provide an air gap, 10. The coil 2 energized by direct current from the battery 3 constitutes a source of flux for producinga maze netic bias in core 1. The energization of coil 2 can be regulated by the adjustable resistance 4 and switch 5 in series with said coil 2 and with a choke coil 14 the function of which is to 'suppress current alternations. The coil 6 is connected in series with a source of direct current, such battery 7, a switch 8,. an output im pedance 9, an adjustable resistance 10 and a vibrator coil 11, which, as shown, is positioned in the air. gap 1c. Said coil 11 is rigidly attached to a vibrator, which may be an acoustical vibrator such as a tuned reed spring or the like 12 which is rigidly carried by an adjustable clamping device 13 by which the coil 11 can be adjusted to the neutral position in air gap 10. Coil 11 is so wound that its turns intersect the magnetic flux between poles la and 1b approximately at'right angles and that the flux exerts on the current in the coil an electrodynamic force in the direction of vibration of reed 12. It will beunderstood that the current flowing through coil 6 is both alternating and direct, the direct current being supplied by battery 7 and the alternating current by coil 11. The battery 3 may be dispensed with as coil 2 may be energized by battery 7 or from the following explanation. The operation of the apparatus shown in Fig, 1 depends upon interacting magnetic, electrical, and mechanical forces. j

The flux, it, in the electromagnet 1 is pro duced first by a constant current 112 flowing through the coil 2. The intensity of this current is known and determined by the F. of 3 and the resistance of 4. Fluctuations are prevented by choke 14. The inductance of'2 is of the known magnitude L2. A second part of the flux is produced by the unknown output current is flowing through the combined inductance of coils 6 and 11. We call this combined inductance, L. Since L varies slightly with the position of the vibrator coil 11, we assume that it has been measured in the neutral position of 11. Thus the flux equation becomes:

L L. =FZ12+F616:P212+P16 q- 1 Where 122 is the effective number of turns in coil 2, and 7L6 is the effective number of turns in coils 6 and 11, and

p: n -P We call the E. M. F. of battery 7, E; the total electric impedance of the output circuit 6, 8, 9, 10, 11, Z; we denote differentiation with respect to time by a prime, and find from Kirchhoffs law for the voltage in the output circuit:

Where (116 5) is the rate of change of induction flowing through the windings: of coils 6 and 11 and producing a counter-E. M. F. according to Maxwells law.

If H is the field strength of the magnetic flux through coil 11; if b is the total effective length of all the windings of the coil 11, measured in a direction at right angles to the flux and at right angles tothe direction of vibration of coil 11 and spring 12; if 1111 is the elongation of coil 11 in the vertical direction of vibration; if S is the effective stiffness of the vibrating system, F its effective viscous friction coefiicient and M its effective mass;-then we find as condition of dynamic balance:

" Thev first term of equation 3 is the electrodynamic force, the other terms are mechanical force reactions due to stiffness, friction and inertia.

f'We eliminate and simplify Equations 2 and 3.

The field strength H 'of the approximately homogeneous field between the magnet poles is equal to the flux divided by the area of the pole faces. Hb therefore equals the flux qh, divided by the heightof the pole face in the direction of vibration and multiplied by the number m1 of coil windings crossing the entire length of the pole face at right angles to the direction of vibra tion. Windings which cross only a part of the pole face are counted with proportionally reduced weight. The dimension of H1) is that of a flux, divided by a (known) length, which-we call It. Therefore we have:

In the differential Equations 7 and 8 we know all quantities but is and 11, which are unknown functions of time and which can be calculated from said equations, subject to boundary conditions. Since we are only concerned with proving the ability to sustain vibrations at all, we may assume that the solution will be an infinitely small vibration*,superimposed to a constant deflection; and accordingly, from the electrical viewpoint, an A. C. of minute amplitude superimposed to a D. C. In this case we may neglect all harmonies of the fundamental oscillation. The solution of 7 and 8 can then be written, in symbolical form:

is=io+id Eq. 9a and The constant components of current and deflection are easily found. From 7 we have:

where Z0 is the D. C. value of the known circuit impedance Z. In the same way we find from 8:

Having thus determined direct current and constant spring deflection, we investigate the A. C. components of the fundamental circular frequency w: From '7 we find: on account of i" 7'w (Eq. 15) and y.=y7'w (Eq. 16):

-z1'-Li wyjw -l =o E 14 From 8 wefind:

By demanding a solution of the form given by Equations 9a and 9b we have introduced the new unknown w. We therefore cannot expect to solve both 14 and 17 for i/y and find, from 14:

By equating 18 to 19 we find an equation which contains 1.0 as the only unknown quantity:

v (b2 z+p o)-(pg z+ p o)= q- 20 The solution of 20 is restricted to real values of w, since we demand harmonic vibrations of j' means :thatinstead or trying to express theirequency by arbitrary circuit constants we 1,977,939 amplitude. We cantherefore split 20 into two independentequations'by equating the imaginary andthe part of 20 separately to zero. For this purpose we divide the' lm'own imand areactive componenti j 5 pedancefZ of theoutputcl-rcuit into a resistive utilize the ,known frequency .for the purpose of determining circuit [conditions favorable to sustained oscillations.

By substituting Equations 2-1 and 22 into window-( mwhe q- The imaginary part of 23 gives us:

"positive quantities. Therefore the factors of i the right side must .be either both positive or both negative. 1

Further information asJtorthe value of these factors, which represent magnetic fluxes, is obtained, when we divide Equation .26 by Equation 13, which gives us;

'In view of the relation between L and p (Equation 1) we can rearrange '27 into:

; 'I'he left .side of 28 is the quotient of a friction force by stiffness force, It is therefore of the .same order. of magnitude as the damping factor of the spring; that is, much smaller than one.

The right .side of .28 is the; product of two factors, at least one of which will also have to be much smaller than order to satisiy the equation v The first .of these factors is the quotient of the inductive impedance of coils :6 and 11, by the effective circuit resistance. Making this factor small by an increase of external ohmic resistance would result in a my inefllcient apparatushbe "cause a @generatorzproducm a maximum output when internal and external impedances are equal.

without loss in efliciency by iantiresonant tuning or circuit impedances.

"We conclude therefore that the absolute value of the second factor must be much smaller than one:

Consequently, mi: is approximately equal to -in 0. makes the second factor on the right side of Equation 26, pitta-H2120, negative. There- 'fore, the other factor must also be negative, or miz+2pio o .Eq. 30

We .find therefore, that undamped oscillations of the exact frequency can be produced when :the direct current component of thexfiux produced by coil-6 ((znul) is opposed to the flux produced by coil 2 ((322m) and is smaller than one-half of the latter.

The circuit conditions derived :above are requirements for an undamped oscillation of infinitely small amplitude and the exact frequency I .of Equation 22. If we solve the circuit Equation 23 with the assumption of a fictitious damping coefficientlarger than the :actual one, we find circuit constants which generate a vibration with increasing amplitude. The ultimate balance in that case is achieved by second order efiects like magnetic saturation, hysteresis losses, and harmonic overtones,-.et.c.

' Since, :by observing the requirements of Equations '25, 29., and 30, it possible to produce oscillations of the exact frequency according to 22:;-*it will be so much easier to generate oscillations, if the frequency requirement is eased to that :of vibrations at a frequency close to the natural period of the spring. We will then not :be forced to adhere strictly to the impedance requirement 25. We can, instead find a more gen-- eral solution of the {circuit Equation 20, subject, of course, to the restriction of a real value of w. It is easy to see that real solutions can always be found .by making the phase angle of the electrical impedance (L+Z/9Zw) equal and opposite to the phase angle of the mechanical impedanc Briefly described, the act-ion of the oscillator, shown in Fig. 1, is as follows: As coil 11 .is in a position of unstable balance between the me- .chan'ical force of reed stiffness and the electro- -dynamic force exerted by the magnetic flux on the current in coil 11., any small vmotion of the reed, 12 produces in coil .11 an induced electromotive force which changes the current intensity in coil 6 and thereby .afiects the magnetic flux in such a way that the motion of reed 12 is amplified intoan oscillatory vibration, if the circuit constants are adjusted within the proper amplitude and phase range. t

As shown in Figure" 2, the vibrator 15, here shown as a tuning fork, "is secured rigidly at one end by a clamp '16. Said fork 15 is made of iron or other magnetizable material and is part of an electr c-magnet as will appear presently. An

iron armature 17, secured in position by a clamp 1.8, has poles 17a and 17b disposed at the free and is looselyass'ociate'd with vibrator 15 whereby not to impede or participate in the vibrations thereof. .The air gaps. 29. 1and 30 remainsubstantially. constantin length.during.the vibration. Coils 20 and 21, are mounted on 'pole pieces 17a and 171). Coils 19, 20 and 21 are connested in series through a battery or other source of direct current 22, a variable resistance 23, a

switch 24, and an output circuit here shownas .a; transformer 25.

Coil 19 carries .both direct current and alternating, the formerbeing supplied from the-battery 22 and the ,latter from the coils 20 and 21. The alternating current component in coil 19' is tuned by variable conjdenser26. vThe apparatus as .shown may be a tuned amplifier of electrical variations supplied to the input circuit which; as here shownj'comprises an iron core 2'7and a coil winding 28. If the circuit constants are such that the vibration losses are nearly but not completely compensated,

the apparatus will serve as a sharply tuned amplifier for both mechanical and. electrical oscillations of the resonant frequency of vibrator 15. For example, if a small amount ofvelectricalenergy at or near the resonance frequency is supplied to the input circuit .28, it will cause relatively violent vibrations of fork 15 and corre- .spondingly amplified electrical output energy at tion value and maintained thereat by the battery 22 or any other suitable powerysupply.

r --Since poles 15a and'15b of the vibrator 15 have opposite directions with respect to theflux and also to motion, coils 20 and 21 assist each other as far asthe vibratoryinteraction is concerned. The symmetrical arrangement of coils 20 and 21 tends to reduce the harmonic content of both mechanical and electricaloscillations. Due'to the inverted arrangement. of poles 17a and 17b of ironcoreas shown, the latter oppose each other and therefore their inductance coefficient is small. However, this inverted arrangement is not necessary. v

The embodiment shown'in Figure 2 differs i'n two important structural respects from the embodiment shown in Figure 1. Firstly, as shown in Figure 2, the coils 20 and 21 are stationary and the electro-magnt, constituted by. the fork 15 and coil 19, is movable, whereas as' shown in Figure 1, the coil 11 is movable and the electromagnet, constituted by the core 1 and coil 6, is stationary. The arrangement shown in Figure 2 is preferablein this respect since it is somewhat difficult to properly secure a coilto an acoustical vibrator. Secondly, as'shown in Figure 1, coil 2 is provided in order to effect the proper phase relation between vibratory motion and the fundamental frequency of electrodynamic force. This can be accomplished more economically by changing the alternating current impedance relations between the electrical circuit elements as, forexam ple by tuning the magnetizing coil 19 in Figure 2 by the shunt condenser 26. Thus,

while I prefer the arrangement shown in Figure 2, the phase'relation between vibratory motion and the fundamental frequency component of electrodynamic force may be adjusted. by the magnetic biasing coil 2 or by tuning the magnetizing coil inductance 19. It will be noted that by the present invention I have eliminated the "parting from the basic principles of the invenand subjected to .the action of'saidflux, said. secc'oil secured to said vibrator disposed for movenecessity for electronic tubes or other spacedischarging devices, andinthis connection it .will ,be-observed that in the apparatusshown in 'Fig.

bilateral conductivity! V While I haveshown two preferredeinbodiments of the invention, it 'will'be obviousto' those skilled in the art that changes in the parts and the arrangement thereof may be made without detion. For example, tuning reeds and forks may 'be' replaced by diaphragms; air columns, crystals andthe like; and the electrodynamic force-exert'ed in the operation of the apparatus may be replaced I by another electro mechanical .force, such as electromagnetic, electrostatic, piezo-ele'ctrio and magnetostrictive and like forces. Also, electromagnetic induction can 1 be :replaced'. by electrostatic, piezo-electric andequivalent reactions. Accordingly, I do not wish to' be limited to the specific embodiments shown except as may be required by the appended claims and the priorart. Y

Having thus described my invention, what I claim is: I .105 1. Apparatus comprising a vibrator having a resonant frequency, an electro-magnet having an air gap, a current carrying coil secured to said vibrator disposed for movement in said air gap, an energizing winding "for said electro-magnet 1w energized from said first mentionedcoil, a source of direct current forsaidwinding, and means for producing direct current flux in said magnet independent of said winding.

2. An electro-mechanical ,vibratorysystem 1 comprisinga magnetizable core, a first winding 0nd winding being relatively movable with respect to said core underthe control of said vibrator whereby electrical energy variations are induced stationary winding, said, movable winding having electrical energy variations induced therein by movement thereof under the control of said vibrator in the field of said core for varying the "magnetizing action of saidfirst mentioned windn a 4. Apparatus comprisinga vibrator, an electromagnet having an air-' gap,'a current carrying ment in said air gap, an energizing windingfor said electro ma'gnetenergized-from said first mentioned coil; and" means for adjusting the phase relation between the-'v-ibratory'motion of i said vibrator and'the frequency component of the "flux ofwsaid electro-magnet. i

5."An electro-mechanical vibratory apparatus 50 comprising a first winding, a source of electrical energy, means including said winding and source of energy for producing a magnetic field, a mechanical vibrator, and a second winding in series with said first winding, said second winding being relatively movable in said magnetic field under the control of said mechanical vibrator CARL FICHANDLER. 

